A substrate processing apparatus is used in the process of manufacturing semiconductors, liquid crystal panels, and the like to supply a treatment liquid (e.g., resist stripping liquid, cleaning liquid, etc.) to a surface of a substrate, such as a wafer or a liquid crystal substrate, to thereby treat the surface. Among such substrate processing apparatuses are those that rotate a substrate horizontally and supply a treatment liquid to a surface of the substrate from a nozzle facing the center of the surface so that the treatment liquid is spread over the surface by the centrifugal force of the rotation. There has been proposed a substrate processing apparatus that performs such spinning operation (e.g., see Patent Document 1).